1. Field of the Invention
The present invention relates to the use of coherent energy pulses as from high-power pulsed lasers in the shock processing of solid materials, and more particularly to a laser rod or slab and method of improving the same for generating more frequent laser pulses in laser peening systems.
2. Description of the Related Art
Known methods for the shock processing of solid materials, particularly known methods for the laser shock processing of solid materials, typically use coherent energy from a laser beam oriented near normal to a workpiece.
Typical laser shock processing techniques and equipment can be found in U.S. Pat. No. 5,131,957 to Epstein.
An operational effect and use of such laser shock processing systems is that to decrease operational costs, there is a necessity to generate more laser pulses per unit of time. In order to accomplish this goal, it is necessary to fire the laser flash lamps more frequently, thereby putting forth more heat into the Nd glass gain medium of the laser amplifiers. The convectively cooled medium develops thermal gradients which cause surface tensile stresses. These stresses are intensified at flaws along the surface of the Nd glass medium, and therefor cause fracture of the medium. An illustration of surface flaws in a glass rod is shown in FIG. 1.
Particular flaws in such laser rods include the natural surface finish and manufacturing accidents, such as accidentally bumping the edge of the glass medium or improper fixation of the medium during cutting, or other manufacturing steps. Such flaws act as stress risers along the surface of the amplifier laser rod or slab causing, at that location, a crack to initiate.
What is needed in the art is a laser rod or slab which may prove to have an ability to withstand thermal stress of use by reducing the flaws on a surface finish of amplifier rods and slabs.
The present invention comprises a laser rod or slab and method of manufacturing of the laser rod or slab for use in a laser peening system. Generally, the concept revolves around reducing the stress risers along the surface of the amplifier laser rods or slabs.
The invention, in one form thereof, is a laser peening system comprising a phosphate glass laser amplifier rod or slab, having an absence of surface defects larger than about 50 xcexcm, whereby the surface finish permits the laser peening system to operate at a rate of at least two peening operation per second.
The invention, in another form thereof, provides a laser peening system as described above, in which the laser rod or slab is operated in excess of 20 watts per centimeter average power.
The invention, in another form thereof, provides a phosphate glass laser amplifier rod or slab having substantially no platinum inclusions therein.
An advantage of the present invention, is that by reduction of the surface flaws, an increase in the repetition rate of the laser system is possible, thereby reducing the costs of laser peening.
Another advantage of the present invention is that by reducing surface flaws, the laser rod or slab of the present invention has a reduced chance of cracking as it is utilized.
A further advantage of the invention is that by utilization of the present method, a change in the stress concentration of the laser rod or slab is created so that the concentration is more even, thereby blunting stress risers which may cause crack initiation.